/* eslint-disable no-undef */
/* eslint-disable no-new */
/* eslint-disable no-unused-vars */
class Compiler {
  constructor (vm) {
    this.el = vm.$el
    this.vm = vm

    this.compile(this.el)
  }

  // 编译模版，处理文本节点和元素节点
  compile (el) {
    const { childNodes } = el

    Array.from(childNodes).forEach(node => {
      if (this.isTextNode(node)) {
        this.compileText(node)
      } else if (this.isElementNode(node)) {
        this.compileElement(node)
      }

      // 判断node节点是否有子节点，如果有子节点，需要递归调用
      if (node.childNodes && node.childNodes.length) {
        this.compile(node)
      }
    })
  }

  // 编译元素节点，处理指令
  compileElement (node) {
    Array.from(node.attributes).forEach(attr => {
      let { name: attrName, value: key } = attr

      if (this.isDirective(attrName)) {
        // v-text => text
        attrName = attrName.substr(2)

        this.update(node, key, attrName)
      }
    })
  }

  update (node, key, attrName) {
    const updateFn = this[`${attrName}Updater`]

    updateFn && updateFn.call(this, node, this.vm[key], key)
  }

  htmlUpdater(node, value, key) {
    node.innerHTML = value

    new Watcher(this.vm, key, newValue => { node.innerHTML = newValue })
  }

  // 处理 v-text 指令
  textUpdater (node, value, key) {
    node.textContent = value

    new Watcher(this.vm, key, newValue => { node.textContent = newValue })
  }

  // 处理 v-model 指令
  modelUpdater (node, value, key) {
    node.value = value

    new Watcher(this.vm, key, newValue => { node.value = newValue })

    // 双向绑定
    node.addEventListener('input', () => {
      this.vm[key] = node.value
    })
  }

  // 编译文本节点, 处理差值表达式
  compileText (node) {
    const reg = /^\{\{\s*(.+?)\s*\}\}$/
    const value = node.textContent

    if (reg.test(value)) {
      const key = RegExp.$1

      node.textContent = value.replace(reg, this.vm[key])

      // 创建 Watcher 对象，当数据改变，更新视图
      new Watcher(this.vm, key, newValue => { node.textContent = newValue })
    }
  }

  // 判断元素的属性是否是指令
  isDirective (attrName) {
    return attrName.startsWith('v-')
  }

  // 判断是否是文本节点
  isTextNode (node) {
    return node.nodeType === 3
  }

  // 判断是否是元素节点
  isElementNode (node) {
    return node.nodeType === 1
  }
}
